1. Field of the Invention
The present invention relates to a sheathing material for a construction machine and a method for producing the same, and more specifically, to a sheathing material for a construction machine and a method for producing the same, which is suitable for a sheathing material for covering an upper rotating body of a hydraulic excavator.
2. Description of the Prior Art
In the past, as shown in FIG. 3, with respect to a guard cover 52 or a bonnet cover 53 forming a sheathing material for an upper rotating body 51 in a hydraulic excavator 50, plastication has been progressed for the purpose of lightweighting. A workman sometimes gets on the cover 52 or 53 when a front attachment is checked. In case of the guard cover 52 which will be explained, therefore, a lifting step 52a is formed on the front surface of the guard cover 52. In order that when the workman gets on the guard cover 52, the step 52a and a top plate 52 are not greatly flexed, a reinforcing number 54 formed from a steel plate, a pipe and the like is mounted on the inner surface of the guard cover 52 to make up for insufficiency of rigidity.
However, since in the conventional guard cover 52, the reinforcing member 54 has to be used, there poses a problem that the number of parts increases to increase costs. Further, since the reinforcing member 54 is formed of metal, the weight of the entire cover guard 55 is not lightweighted so much as compared with the case where the guard cover is made from a steel plate.
The present invention has been accomplished in consideration of the problem as noted with respect to the sheathing material for the conventional hydraulic excavator as described above. The present invention provides a sheathing material for a construction machine and a method for producing the same, in which lightweighting can be attained without using a metallic reinforcing member, and even if a load is applied to a top plate for the sheathing material, it is not greatly flexed.
The sheathing material for a construction machine according to the present invention comprises a hollow resined shell molded as a sheathing material for an upper rotating body by rotation molding, and a resin foamed body filled in the resined shell.
The sheathing material in the present invention is integrally formed with depressions or projections, the depressions or the projections being provided with flat surfaces whereby a lifting step can be formed.
The shell according to the present invention can be formed of a resin selected from a group comprising a polyethylene resin, a polycarbonate resin, and a nylon resin.
The resin foamed body according to the present invention can be constituted of a hard urethane foam, whose filling density is preferably not less than 30 kg/m3 but not more than 75 kg/m3.
The method for producing a sheathing material for a construction machine according to the present invention principally comprises; molding a hollow resined shell by rotational molding, and using the molded resined shell as a form into which a resin foamed body adjusted in filling density is filled and set.
The rotational molding in the present invention is a molding method in which a thermoplastic resin powder is charged into a hollow mold, after which the mold is heated while being rotated, a shape is made along the surface of the mold, which is then cooled and solidified while being rotated, and after this the molded product is removed. The rotating the mold termed herein means rotating in accordance with a so-called biaxial rotational method in which both axis of ordinates and axis of abscissae are rotated simultaneously.
According to the aforementioned rotational molding, a mold not requiring pressurization need not to have a high strength, and for example, a steel plate, aluminum castings or the like will suffice. Accordingly, a shell for those having a volume such as a sheathing for a construction machine can be fabricated inexpensively. Further, since the interior of the resined shell is hollow, lightweighting can be attained. Particularly, the sheathing material for a construction machine is large in size and complicated in shape, but if the aforementioned rotational molding is utilized, the shell therefor can be obtained easily. Moreover, the molded resined shell can be satisfied with a shock resistance required by the construction machine.
The sheathing material obtained by filling a resin foamed body formed, for example, of a hard polyurethane foam into the resined shell obtained by the rotational molding to set it has a sandwich construction in which both lengthwise sides of the resin foamed body are sandwiched by resin plates, and the resin foam is adjusted in filling density to be not less than 30 kg/m3 but not more than 75 kg/m3 so that the flexure rigidity of the sheathing material can be enhanced to thereby fulfill with both attainment of lightweighting and enhancement of flexure rigidity.